The homopolymers of maleic anhydride or copolymers based on non-hydrolyzed maleic anhydride are insoluble in water at neutral pH. They become gradually soluble by hydrolysis reaction in aqueous medium, due to opening of the maleic anhydride rings by nucleophilic attack of the water molecules on the anhydride functional groups and subsequent opening of the rings with production of carboxyl functional groups.
Direct solubilization in aqueous medium by hydrolysis of the anhydride functional groups has the disadvantage of being a process which is lengthy and difficult to control. Indeed, it is not known how many anhydride functional groups are consumed in order to "dissolve" the polymer.
Moreover, it is known that the homopolymers or copolymers of maleic anhydride are soluble in certain organic solvents.